A Power Amplifier (PA) is an important component in an electronic device and can amplify the power of a weak electronic signal for the purpose of transmission and emission thereof. Generally, a characteristic curve reflecting a power relationship between an input signal and an output signal of the power amplifier can be divided into a linear region, a nonlinear region and a saturated region as the input signal is increased in power. An output of the Power Amplifier (PA) substantially results from linear amplification of the input signal in a region where the input signal is small in amplitude, but the Power Amplifier (PA) exhibits a nonlinear characteristic gradually noticeable as the input signal is incremented in amplitude so that the output signal will be distorted until it becomes saturated in the end. In the frequency domain, this nonlinearity appears as the output signal with a spectrum including an elevated side lobe and a distorted major lobe, where the elevated side lobe may discourage normal operation of other devices operating in adjacent channels. As new modulation schemes emerge, the envelope of the input signal has an increasing dynamic range resulting in inevitable nonlinear distortion. Therefore, the nonlinear characteristic of the PA has to be technically compensated for to remedy such distortion. Pre-distortion is a working approach for this purpose.
However, a pre-distorter has to operate with a specific coefficient, and if the coefficient of the pre-distorter is acquired adaptively, the coefficient of the pre-distorter can be acquired with an adaptive algorithm only after a transmitter is started to operate. Since the nonlinearity of PA has not been fully compensated for after the transmitter is started until the adaptive algorithm fully converges, the spectrum of the output signal still may have an elevated side lobe which may discourage normal operation of other devices operating in adjacent channels.